This invention relates generally to a fuel delivery system and more particularly to a fuel pressure regulation system for a marine engine.
Electric motor fuel pumps have been used in various ways to deliver fuel to internal combustion engines for a wide range of applications. One such use of electric fuel pumps is in the form of a constant-delivery fuel pump, in which the electric fuel pump is operated at a constant speed with a pressure regulator being used to return excess fuel from the engine to the fuel tank. It should be noted that there are many disadvantages associated with a fuel pump system of this kind. For instance, the returned or excess fuel carries engine heat with it to the fuel tank, thereby increasing the temperature and vapor pressure within the tank. Venting this vapor pressure into the atmosphere causes pollution problems and adversely affects fuel mileage. Additionally, operating the motor at a constant high speed increases energy consumption and reduces the operational life of the fuel pump, fuel filter, and other components.
Another type of fuel pump system uses a feedback loop to control the speed of the fuel pump, the duration of operation, or other operational parameters. Unlike the constant speed excess return pumps previously described, a fuel pump system which incorporates a feedback loop will drive the fuel pump according to the output which is required. U.S. Pat. No. 4,728,264 discloses a fuel delivery system in which a D.C. motor fuel pump delivers fuel under pressure from a fuel tank to the engine. A pressure sensitive switch is responsive to fuel pump output pressure for applying a pulse-width modulated D.C. signal to the pump motor, and thereby controlling pump operation so as to maintain constant pressure in the fuel delivery line to the engine independently of fuel demand. Similarly, U.S. Pat. No. 4,789,308 discloses a self-contained fuel pump that includes an electronic sensor in the pump outlet end cap responsive to fuel outlet pressure for modulating application of current to the pump motor and maintaining a constant pressure in the fuel delivery line. Although the aforementioned fuel delivery systems address and overcome a number of problems present in the art, further improvements are continually being made. For instance, the addition of air to combustible fuel delivered to an injector has proven effective in increasing the atomization of the injected fuel and thus, the quality of the combustion in the cylinder.
An example of this type of direct air-fuel injection system is seen in U.S. Pat. No. 4,693,224 and U.S. Pat. No. 4,825,828. In the fuel delivery systems disclosed in these patents, air is entrained within a premetered quantity of fuel and the mixture is delivered directly to a combustion chamber via the injector. Consequently, a system such as this requires both a fuel rail and air rail and components for introducing elements of those two rails together in some premetered fashion. In this regard, it should be noted that there are certain disadvantages which arise when the pressures maintained in the air and fuel rails are not related to each other, particularly when one of the rails experiences a sudden fluctuation not experienced in the other rail. These conditions may result in an undesirable ratio of fuel and air being supplied to the injector.
Thus, it would be advantageous to provide a fuel delivery system which supplies atomizing air into the fuel in a manner that maintains accurate control of the relative amounts of air and fuel mixed together.
The above-noted shortcomings of prior art fuel delivery systems are overcome by the present invention which provides a fuel pressure regulation system for applications such as those noted above in which improved combustion is achieved by supplying an injector with atomizing air entrained with a premetered amount of fuel. The fuel pressure regulation system of the present invention mixes the air with the fuel based on relative pressures within the air and fuel rails, and comprises a first pressure sensor, a second pressure sensor, a control circuit, and a fuel pump or some other pressure control device. The first pressure sensor measures the air pressure within an air rail, converts the measured air pressure into an electronic signal, and sends this air pressure signal to the control circuit. Similarly, the second pressure sensor measures the fluid pressure within a fuel rail, converts the measured fluid pressure into an electronic signal, and sends this fuel pressure signal to the control circuit. The control circuit is an electronic circuit that generally includes a first stage, a second stage, and an output stage and provides the fuel pump with closed loop control which maintains the fuel rail at a fixed pressure relative to the air rail. Preferably, the control circuit provides closed loop control which entails both proportional and integral control using a pulse-width modulated signal to drive the fuel pump. The fuel pump is in fluid communication with the fuel rail and is operable to adjust the fluid pressure within the fuel rail according to the pulse-width modulated signal sent by the control circuit.
Objects, features and advantages of this invention include providing a fuel pressure regulation system which maintains the fuel rail pressure at a constant pressure relative to the air rail pressure, provides closed-loop control of the fuel pump, supplies a constant air and fuel mixture to an injector, and is of relatively simple design, economical manufacture and assembly and has a long and useful life in service.